In connection with the completion of an oil, gas or water well in preparation for production from such well, it is frequently necessary and appropriate for the operator of the well to place a device known as a bridge plug in the casing of the well in order to segregate productive strata from non-productive strata within the depth pentrated by the well bore. The purpose and function of the bridge plug itself is well known and understood in the art.
In typical practice, in order to assure that no debris or other impediments to insertion of the bridge plug to the desired depth exist within the well casing, a debris removal device commonly known as a "junk basket" is inserted into the well casing and run to a depth below that selected for placement of the bridge plug. When the debris removal operation is completed, the junk basket is removed from the well casing, the bridge plug is inserted and fixed in the well casing at the desired depth.
However, in practice, the junk basket will occasionally encounter debris or other obstructions which cause it to lodge in the well casing above the depth selected for bridge plug placement. in that event, it is necessary to remove the obstruction by inserting a drill bit and drilling through both junk basket and obstruction. When such drilling operation is completed, the debris removal operation must be repeated, and upon its completion the final bridge plug placement operation is initiated.
Because bridge plugs in use in the industry are costly and relatively difficult to drill through should they become lodged in an unsuitable location in the well casing, the separate debris removal and gauging operation with a much less costly and essentially expendable junk basket has been standard practice. Although this standard practice does greatly reduce the risk of the bridge plug becoming lodged in an unsuitable location in the well casing, it suffers the distinct disadvantage of requiring two "runs" or "round trips" through the casing to place a single bridge plug. Such repetitive operations significantly lower the efficiency and increase the cost of bridge plug placement.
In recognition of that disadvantage, attempts have previously been made in the industry to combine the cleaning and gauging operation with the bridge plug placement operation, so that only a single run down the well casing is necessary. Such previous attempts have consisted primarily of merely fixedly attaching a junk basket device to the bottom of a bridge plug and concurrently introducing them into the well casing. The effectiveness of such attempts has been only marginal, however, in that they have achieved successful debris removal and bridge plug placement in a single operation only in those instances in which no obstruction to downward travel of the combined apparatus is encountered. When such obstructions are encountered, both junk basket and bridge plug become lodged in the casing in an unsuitable location for bridge plug placement. Upon such occurance the well completion operations cannot be continued until a drill bit is inserted into the casing to drill through both bridge plug and junk basket. Bridge plugs in common use in the industry are constructed of materials highly resistant to such drilling, making the drilling operation costly in terms of time as well as wasteful of an otherwise undamaged bridge plug. Thus, previous attempts to achieve concurrent debris removal and bridge plug placement reflect only an assumption of risk in return for the possibility of significant improvement in completion efficiency.
From the foregoing, it is apparent that a device and method to achieve the efficiency of concurrent debris removal and bridge plug placement while avoiding the high risks associated with previous attempts was needed and desired by the industry.